A conventional binocular night vision device uses a pair of monocular night vision scopes which are mounted and associated with one another in such a way as to provide the user of the device with binocular vision, thereby allowing the user to have a night-time view with depth perception. FIG. 1 shows a night vision device 10 including a pair of night vision monoculars 12 which can be suspended in front of a user's eyes by an elongated shelf 14 which has a laterally rectangular shape in plan view, and is also of a generally rectangular shape in both frontal and side elevation views. Depending from the shelf 14 is a pair of spaced apart mounts 16 (best seen in FIG. 7b). FIG. 2a shows a top view of shelf 14 without the binocular mounted onto it. FIG. 2b shows a bottom view of shelf 14 without the binocular mounted to it.
The interpupillary distance (IPD) is defined as the distance between the user's pupils. In order to allow adjustment of the horizontal spacing between the monoculars 12 to match the interpupillary distance (IPD) of a user, an IPD adjustment mechanism moves the monoculars toward each other and away from each other. Part of the IPD mechanism is located on the outside of shelf 14 and part of it is located between walls of shelf 14. The walls are underneath shelf 14.
As shown in FIGS. 2b and 3, the underneath part of shelf 14 is divided into three sections 34, 36, 38 by four walls 18, 20, 22, and 24. A circular aperture is located inside each of the walls. Aperture 18a is located in wall 18, aperture 20a is located in wall 20, aperture 22a is located in wall 22, and aperture 24a is located in wall 24. Rotatably received in the apertures 18a, 20a, 22a, 24a are flanges 18b, 20b, 22b, and 24b of an eccentric shaft 26. Eccentric shaft 26 is a thin elongate blade portion. Inside each of the flanges 18b, 20b, 22b, 24b are off-center apertures 18c, 20c, 22c, and 24c. A pivot lever 28 of the eccentric shaft 26 is part of flange 18b and extends outwardly of one end of the shelf 14.
Rotatably received in apertures 18c and 20c is an IPD threaded shaft 30. A monocular (not shown) is mounted onto IPD threaded shaft 30. One end of IPD threaded shaft 30 extends through aperture 18c in flange 18b, which is in aperture 18a of wall 18. Consequently, this end of IPD threaded shaft 30 extends from the space in section 36 at the underside of shelf 14 to the outside of wall 18. The other end of IPD threaded shaft 30 extends through aperture 20c in flange 20b, which is in aperture 20a of wall 20. Consequently, this end of IPD threaded shaft 30 extends from space 36 at the underside of shelf 14 into the space in section 38 at the underside of shelf 14.
Rotatably received in apertures 22c and 24c is an IPD threaded shaft 32. Another monocular (not shown) is mounted onto IPD threaded shaft 32. One end of IPD threaded shaft 32 extends through aperture 24c in flange 24b, which is in aperture 24a of wall 24. Consequently, this end of IPD threaded shaft 32 extends from the space in section 34 at the underside of shelf 14 to the outside of wall 24. The other end of IPD threaded shaft 32 extends through aperture 22c in flange 22b, which is in aperture 22a of wall 22. Consequently, this end of IPD shaft 32 extends from space 34 at the underside of shelf 14 into the space in section 38 at the underside of shelf 14.
The end of IPD threaded shaft 32 that extends into space 38 from space 34 is threaded and carries a washer member 40 which is secured axially on the IPD threaded shaft 32 by a threaded nut 42. Consequently, IPD threaded shaft 32 cannot move out of aperture 22c in flange 22b. The end of IPD threaded shaft 30 that extends into space 38 from space 36 is threaded and carries a washer member (not shown) which is secured axially on the IPD threaded shaft 30 by a threaded nut (not shown). Consequently, IPD threaded shaft 30 cannot move out of aperture 20c in flange 20b. 
The end of IPD threaded shaft 32 that extends from space 34 to the outside of wall 24 is attached to a control knob 40. The end of IPD threaded shaft 30 that extends from space 36 to the outside of wall 18 is attached to a control knob 42. Each of the monoculars is respectively coupled to the IPD shafts 30 and 32. Control knobs 40 and 42 may be rotated independently of each other. When control knobs 42 and 40 are rotated, they may respectively cause IPD shafts 30 and 32 to rotate thereby moving the monoculars toward and away from each other to adjust for varying eye separations.
As explained above, lever 28 is part of flange 18b. Each of the flanges are connected together by the eccentric shaft 26. Each of the flanges has an off-center aperture. Off-center apertures 18c and 20c receive IPD threaded shaft 30 and off-center apertures 22c and 24c receive IPD threaded shaft 32. Rotation of lever 28 rotates eccentric shaft 26, flanges 18b, 20b, 22b, and 24c, shaft 30 and shaft 32 relative to shelf 14. Since each of monoculars are coupled to shafts 30 and 32, rotation of lever 28 tilts each of the monoculars relative to shelf 14 and relative to a user's eyes. Thus, the main purpose of the eccentric shaft 26 and its associated flanges is to provide a means of tilting the line-of-sight of the two monoculars simultaneously. The lever may be used to adjust the tilt of the monoculars to align with the user's line-of-sight.
As shown in FIG. 3, the conventional eccentric shaft uses an o-ring 46 to provide rotational friction between the eccentric shaft 26 and the shelf 14. The o-ring 46 is placed in a groove 18d of flange 18b, near adjustment lever 28. After the eccentric shaft is assembled to the shelf assembly, the purpose of the o-ring is to provide frictional resistance against the shelf. The rotational friction force occurs between o-ring 46 and aperture 18a of wall 18 when flange 18b is inserted into aperture 18a. Thus, the o-ring acts as a frictional resistor between the eccentric shaft and the shelf. The frictional interface between o-ring 46 and aperture 18a is controlled by tight tolerances between flange 18b of the eccentric shaft 26, the shelf 14, and the o-ring 46. One of the purposes of the rotational friction provided by the o-ring is to minimize or prevent the night vision binocular from inadvertently tilting because of vibration during operation. Another purpose is to provide a smooth resistance during adjustment.
However, it is possible for the eccentric shaft to rotate during vibration and overcome the frictional resistance provided by the o-ring. This can cause the night vision goggles' optical axis to tilt downward.
It is therefore necessary to provide a design that prevents, or at least better inhibits, the eccentric shaft from rotating during operation.